In printing machines, it has hitherto been customary to feed sheets manually one by one or, when sheet feeding is mechanized, to pile sheets in a stack in a hopper disposed behind the printing machine, to be successively fed to the printing machine automatically.
In a printing machine, the sheet is moved upwardly to the printing position, and the sheet on which printing has been made is ejected onto a position above the sheet feeding tray, with the result that a sheet receiving tray is located above the sheet feeding hopper. Thus, printing machines of the prior art automatically receiving a supply of sheets have had the disadvantage that it is impossible to readily replenish the sheets on the hopper by supplying them from the front of the machine when the stack of sheets on the hopper are reduced in number.
In a printing machine such as a typewriter, printing means is located on the side of the operator, and a sheet fed from the rear of the machine by way of the lower portion of the machine is moved upwardly in the front of the machine after characters or symbols are printed thereon. Stated differently, the sheet moves along the front of the machine in a printing operation, and guide plates and other elements are located to form a wall, as it were, where a sheet moves. Thus, the idea of supplying sheets to the hopper from the front of the printing machine have not occurred to anyone in the past.
When sheets are supplied to the hopper from the rear or side of the printing machine by keeping clear of the ejected sheet receiving tray located in the front upper portion of the machine, it is necessary to put the sheets in an orderly manner on the hopper in order to ensure that sheet feeding is carried out satisfactorily. It is a timeconsuming operation to put loose sheets are skewed or not located in the correct position on the hopper.
When sheet feeding is carried out automatically, a portion for supporting sheets to be fed is disposed in a lower position and a portion for receiving sheets after being printed is disposed in a higher position. A guide plate or other means will naturally be used for guiding sheets from the platen to the ejected sheet receiving portion. Automation of sheet feeding makes such structure necessary, and consequently it becomes impossible to manually feed one sheet to the platen when it is required to produce only one copy or it is desired to run the printing machine for test. Even if it is not impossible to do so, the operation would be troublesome because detaching of some part from the apparatus would have to be effected.
In a printing machine, a sheet is passed along the platen and moved upwardly from below in front of the printing head before being wound on the platen. The sheet would on the platen is not held stably unless a portion of the sheet above the printing head is kept close to the platen. To this end, the sheet would on the platen is generally held against the platen by means of a paper bail. However, the paper bail interferes with an operation of inserting a sheet. To eliminate this disadvantage, a paper bail arm supporting the paper bail has hitherto been moved manually. More specifically, when a sheet is inserted, it has been customary to move the paper bail away from the platen and to move the paper bail toward the platen upon completion of insertion of the sheet, to make the printing machine ready for a printing operation.
The advent of automation of a sheet feeding operation in a printing machine has created a demand for automatically moving the paper bail toward and away from the platen so as to avoid its interfering with the insertion of a sheet.